Anti-dsDNA antibodies (Abs) are one of the diagnostic criteria of systemic lupus erythematosus (SLE). To understand how these autoAbs are regulated in healthy individuals and to identify the mechanisms underlying their expression in autoimmunity, we have used an immunoglobulin transgenic (Ig Tg) model. The advantage of this model is that the development of anti-dsDNA B cells can be tracked in the context of a diverse B cell repertoire in non-autoimmune and autoimmune-prone (lpr/lpr) backgrounds. We present data showing that T cells play a determining role in the phenotype of anti-dsDNA B cells. Using Ab depletion to remove CD4 cells, we have demonstrated that the phenotypic changes in anti-dsDNA B cells in Fas-deficient mice - their follicular entry and maturation - are dependent on T cell help. Additionally, using a model system to provide T cell help, we can induce follicular entry, maturation, and Ab production from anti-dsDNA B cells in Fas-sufficient mice. Collectively, these results suggest that the availability of T cell help is responsible for determining whether anti-dsDNA B cells are functionally silent or become activated. Finally, we have identified unique attributes of the lpr/lpr dendritic cells (DCs) that we hypothesize play a central role in generating the (auto)reactive T cell help in vivo. Here, we propose to extend these preliminary findings to identify first, the nature of the CD4 T cell help in young Fas-deficient mice that promotes follicular entry but not terminal differentiation of anti-dsDNA B cells, and the requirements for T cell help in promoting autoAb production in 10-week-old animals. We will test the ability of distinct classes of T cells to provide T cell help to BALB/c anti-dsDNA B cells in Fas-sufficient mice and to alter the kinetics of autoAb production in lpr/lpr mice. Second, we will examine DC function in lpr/lpr mice, and determine the extent to which alterations in DC phenotype in lpr/lpr mice are involved in the initiation of autoimmunity or are secondary to the dysregulation of T and/or B cells. Defining the processes that release certain self-reactive B cells from their tolerant state is critical to the understanding and eventual treatment of autoimmune disease.